This application claims the benefit of Korean Application No. 2001-74200 filed Nov. 27, 2001, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates, in general, to linear compressors for refrigerating systems and air conditioning systems, such as refrigerators and air conditioners, and, more particularly, to a linear compressor provided with an anti-collision device preventing a movement of a piston, which exceeds an upper dead center position of a piston inside a cylinder.
2. Description of the Prior Art
As is well known to those skilled in the art, a compressor is a machine that sucks and compresses the gas refrigerant in a refrigerating system or an air conditioning system, such as a refrigerator or an air conditioner, operated by performing a refrigeration cycle. Compressors have been typically classified into two types: reciprocating compressors and rotary compressors. The reciprocating compressors compress the gas refrigerant by a rectilinear reciprocation of a piston, while the rotary compressors compress the gas refrigerant by rotation of one or more vanes. A linear compressor is a type of reciprocating compressor, and linearly reciprocates a piston using a linear motor to compress the gas refrigerant Such a linear compressor has low energy loss, thus being high in energy efficiency in comparison with the other type of compressors.
FIGS. 1 and 2 are side sectional views, showing the construction of a conventional linear compressor. FIG. 1 shows the linear compressor when a piston is positioned at a stop position, and FIG. 2 shows the compressor when the piston is positioned at an upper dead center position.
As shown in FIGS. 1 and 2, the conventional linear compressor comprises a drive unit 10 and a compressing unit 20, which are housed in a hermetic casing 1. The drive unit 10 generates drive power when electricity is applied from an external power source, while the compressing unit 20 sucks the gas refrigerant and compresses the gas refrigerant using the drive power transmitted from the drive unit 10.
The compressing unit 20 comprises a hollow cylinder 21 defining a compressing chamber 22 in a cylindrical bore with a cylinder head 23 assembled including an end of the hollow cylinder 21 which guides the suction and the discharge of the gas refrigerant. A piston 24 is movably received in the compressing chamber 22 of the hollow cylinder 21, and linearly reciprocates in the compressing chamber 22 using the drive power transmitted from the drive unit 10.
The drive unit 10, which is a type of linear motor, comprises a cylindrical white iron assembly 11 arranged around the hollow cylinder 21. A core 12, wound with a coil 13, is arranged such that the core 12 and coil 13 surround the iron assembly 11 with an annular gap defined between the iron assembly 11 and the core 12. When an alternating current AC is applied to the coil 13 of the core 12, the core 12 generates a magnetic flux. A magnet 14 is positioned in the gap formed between the iron assembly 11 and the core 12 such that the magnet 14 reciprocates along with the piston 24.
The core 12 is fabricated by closely layering a plurality of steel sheets, and is supported by both the hollow cylinder 21 and a support frame 21a. The magnet 14 is mounted to a movable member 25 integrated with the piston 24 into a single structure, and linearly reciprocates in cooperation with the magnetic flux generated by the core 12. Due to the linear reciprocating action of the magnet 14, the piston 24 reciprocates in the hollow cylinder 21.
Both the drive unit 10 and the compressing unit 20 are elastically suspended in the hermetic casing 1 by a plurality of coil springs 2 elastically supporting the hollow cylinder 21 at a lower portion inside the hermetic casing 1. A plurality of spacers 4 vertically extends upward from an upper surface of the support frame 21a of the hollow cylinder 21 to the same height. A resonant spring 3, which is a type of plate spring, is mounted to ends of the spacers 4. The movable member 25, which is integrated with the piston 24 into the single structure and reciprocates by the drive unit 10, is mounted at an end to the center of the resonant spring 3. The piston 24 linearly reciprocates in the hollow cylinder 21 by both the resonant spring 3 and the movable member 25, thus sucking the gas refrigerant into the hermetic casing 1 and compressing the refrigerant prior to discharging the compressed gas refrigerant from the hermetic casing 1.
The cylinder head 23 has a suction chamber 6 and an exhaust chamber 8. The suction chamber 6, which is provided with a suction valve 5, guides the gas refrigerant from the outside of the hermetic casing 1 into the compressing chamber 22. The exhaust chamber 8, which is provided with an exhaust valve 7, guides the compressed gas refrigerant from the compressing chamber 22 to the outside of the hermetic casing 1.
When an alternating current AC is applied to the coil 13 of the drive unit 10, the coil 13 generates a magnetic flux. This magnetic flux of the coil 13 cooperates with the magnetic field of the magnet 14, which is mounted to the movable member 25, thus allowing the movable member 25 to reciprocate in a vertical direction while vibrating the resonant spring 3. The piston 24 thus linearly reciprocates in the cylinder 21. When the piston 24 moves from a stop position of FIG. 1 to a lower dead center position during a reciprocating action, the suction valve 5 is opened to suck the gas refrigerant from the suction chamber 6 into the compressing chamber 22. When the piston 24 moves to a upper dead center position as shown in FIG. 2, the suction valve 5 is closed and the exhaust valve 7 is opened to discharge the compressed gas refrigerant from the compressing chamber 22 to the exhaust chamber 8.
The natural frequency of the resonant spring 3 according to the mass of the piston 24, magnet 14 and movable member 25 is set to be almost equal to the frequency of the alternating current AC applied to the coil 13 of the core 12, and the drive unit 10 can generate high drive power caused by resonance. The amplitude of both the reciprocating piston 24 and the movable member 25 is regulated by controlling the applied voltage. In such a case, to allow the piston 24 to stably reciprocate with a predetermined amplitude, a separate control unit (not shown) capable of stably controlling the amplitude of the piston 24 can be provided.
In such a conventional linear compressor, the volumetric efficiency of the compressor varies in accordance with a gap volume determined by a minimum gap distance Xc between the cylinder head 23 and the upper dead center position of the piston 24. That is, higher volumetric efficiency of the linear compressor can be obtained as the minimum gap distance Xc is reduced. Therefore, when high volumetric efficiency of the compressor is desired, reducing the gap volume as much as possible by controlling the amplitude of the piston 24 such that the piston 24 can approach close to the cylinder head 23 and the suction valve 5 during an operation of the compressor is preferable.
However, during a reciprocating action of the piston in the cylinder of the conventional linear compressor, the behavior of the piston may become unstable, thereby abruptly and rapidly increasing the amplitude of the piston due to unexpected internal or external causes, such as unexpected rapid variation in the applied voltage or unexpected rapid variation in the pressure of the refrigeration cycle. When the amplitude of the piston rapidly increases as described above, the end of the piston may come into collision with the suction valve and/or the cylinder head, thus generating operational noise, in addition to causing serious damage and breakage to the cylinder head, the suction valve, the exhaust valve and/or the piston.
Accordingly, a linear compressor for refrigerating systems and air conditioning systems is provided with an anti-collision device preventing a movement of a piston, which exceeds an upper dead center position of the piston in a cylinder, and thereby prevents the piston from colliding with a suction valve and/or a cylinder head, in addition to attenuating the impact caused by such an excessive movement of the piston.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
In order to accomplish the above and other objects, the present invention provides a linear compressor comprising a cylinder, a cylinder head assembled with the cylinder and having at least one valve, a piston received in the cylinder, and a drive unit reciprocating the piston, and further comprising an anti-collision device preventing the piston from moving past the upper dead center position of the piston and thereby preventing the piston from colliding with the cylinder head and the valve.
In a first embodiment, a plurality of spacers extend from a support frame of the cylinder, a resonant spring is perpendicularly mounted to the spacers, a movable member extends from the end of the piston and is assembled at an end of the movable member with a central portion of the resonant spring and is reciprocated by the drive unit, and the anti-collision device is mounted to the spacers while being spaced apart from the resonant spring by a predetermined gap.
In the first embodiment, the anti-collision device comprises: an elastic member mounted to the spacer and provided with a central opening having a predetermined size, and a shock absorbing member set in a central opening of the elastic member, the shock absorbing member having a central hole and being fitted over the movable member at the central hole such that the movable member reciprocates through the central hole.
In the linear compressor, the distance between the shock absorbing member of the anti-collision device and the resonant spring is preferably set to be almost equal to a value calculated by subtracting a minimum gap distance between the cylinder head and the piston when the piston is positioned at an upper dead center position from a distance between the cylinder head and the piston when the piston is in a stop position.
In a second embodiment, the central hole of the shock absorbing member is tapered in a direction toward the cylinder head, thus having a first tapered surface, and the movable member is tapered at a portion thereof between the resonant spring and the anti-collision device, thus having a second tapered surface corresponding to the tapered surface of the central hole.
In such a case, the axial distance between the tapered surface of the shock absorbing member and the tapered surface of the movable member is preferably set to be almost equal to the value calculated by subtracting the minimum gap distance between the cylinder head and the piston when the piston is positioned at the upper dead center position from the distance between the cylinder head and the piston when the piston is in the stop position.
In a third embodiment, the anti-collision device comprises: a first tapered surface formed on a skirt part of the cylinder by tapering the skirt part such that the diameter of the first tapered surface is reduced in a direction toward the cylinder head; and a second tapered surface formed on the piston so as to correspond to the tapered surface of the cylinder.
In such a case, the axial distance between the tapered surface of the cylinder and the tapered surface of the piston is preferably set to be almost equal to the value calculated by subtracting the minimum gap distance between the cylinder head and the piston when the piston is positioned at the upper dead center position from the distance between the cylinder head and the piston when the piston is in the stop position.